1. Field of the Invention
The present invention relates to wireless communication and more particularly, to a method of configuring a carrier in a multi-carrier system.
2. Related Art
Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data communication. In general, a wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available radio resources. Examples of multiple access system include a time division multiple access (TDMA) system, a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
In a wireless communication system, one carrier is considered in general even if a bandwidth is differently set between an uplink and a downlink. In the 3rd generation partnership project (3GPP) long term evolution (LTE), one carrier constitutes each of the uplinks and the downlinks on the basis of a single carrier, and the bandwidth of the uplink is symmetrical to the bandwidth of the downlink. However, except for some areas of the world, it is not easy to allocate frequencies of wide bandwidths. Therefore, as a technique for effectively using fragmented small bands, a spectrum aggregation technique is being developed to obtain the same effect as when a band of a logically wide bandwidth is used by physically aggregating a plurality of bands in a frequency domain. The spectrum aggregation includes a technique for supporting a system bandwidth of 100 mega Hertz (MHz) by using multiple carriers even if, for example, the 3GPP LTE supports a bandwidth of up to 20 MHz, and a technique for allocating an asymmetric bandwidth between the uplink and the downlink.
Each carrier can be operated as a cell. Further, a UE can designate a specific cell as a barred-cell. The UE cannot select or reselect the barred-cell, and it is also prohibited from accessing the barred-cell. A UE can designate a specific cell as a barred-cell in the following several cases. For example, when a System Information Block (SIB) SIB1 of a specific cell indicates cellBarred, when a System Information Block SIB2 of a specific cell has designated the prohibition of access to an attempt to the specific call, when a Radio Resource Control (RRC) connection request rejection message is received from a specific cell, when a specific cell does not support a frequency band supported by a UE, and when a higher layer (i.e., an NAS layer) of RRC releases the RRC connection of a UE after RRC connection, a corresponding cell is designated as a barred-cell.
If one cell is designated as a barred-cell, a UE is unable to select or access the corresponding cell. Accordingly, although a BS instructs the configuration of a specific carrier corresponding to the barred-cell, the UE is unable to configure the specific carrier. Since the UE does not comply with the instruction set by the BS, a problem arises in configuring a carrier. Accordingly, there is a need for a method of efficiently configuring a carrier in a multi-carrier system.